Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Device and method for generating percussive pulses or vibrations for a
construction
machine
FIELD OF THE INVENTION
The invention relates to a device for generating percussive pulses or
vibrations for a
construction machine, and a method for generating percussive pulses or
vibrations for a
construction machine.
BACKGROUND
A generic vibration generator is known from EP 1 728 564 B1. In this known
vibration
generator the working space in the housing is divided by a working piston into
two pres-
sure chambers. Via an inlet and an outlet the two pressure chambers are
selectively
supplied with or discharged from a pressure fluid in an alternating manner so
that the
working piston moves reversibly and generates a vibration. The timed supply
and dis-
charge of pressure fluid into the individual pressure chambers is effected via
a complex
arrangement of ducts in the working piston. Moreover, inside the working
piston a con-
trol piston is supported in a displaceable manner which is able to selectively
change its
position relative to the working piston by means of stops protruding at the
front faces of
the housing in order to unblock or block certain ducts. Hence, the supply and
discharge
of pressure fluid is achieved by mechanical measures, wherein a switch-over of
the
pressure fluid supply and discharge takes place through the given ducts when
certain
switch-over points are reached.
Comparable mechanical control means in vibration generators can also be taken
from
GB-A-920,158, US-A-4,026,193 or US-A-4,031,812 for example. All these known
devices have a working piston and a control piston which, depending on the
respective
position in the housing, open or close certain ducts, whereby a selective
alternating
supply of the two opposite pressure chambers is brought about in order to move
the
working piston.
Devices of such type are time-consuming and costly in production. Moreover,
due to the
duct layout a certain vibration or percussion behavior of the piston is
predefined at a
predetermined pressure level. A change of the vibration frequency and the
percussion
energy are only possible to a very limited extent and in some cases require
laborious
mechanical reworking.
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SUMMARY OF THE INVENTION
The invention is based on the object to provide a device and a method for
generating
percussive pulses or vibrations, with which an increased flexibility with
regard to the setting
and change of the percussion or vibration behavior can be achieved
The invention provides a device for generating percussive pulses or vibrations
for a
construction machine, having a housing, a piston which is reversibly
reciprocable in a
working space in the housing between a first reversal point and a second
reversal point,
and a pressure fluid supply, through which pressure fluid can in each case be
led into and
out of the working space in the region of the first reversal point and the
second reversal
point, wherein the piston can be set into the reversible movement in order to
generate the
percussive pulses or vibrations.
The invention further provides a method for generating percussive pulses or
vibrations for a
construction machine, in which a piston is reversibly reciprocated in a
working space in a
housing between a first reversal point and a second reversal point, wherein,
for the purpose
of generating the percussive pulses or vibrations, the piston is set into a
reversible
movement by means of a pressure fluid and the said pressure fluid is led into
and out of the
working space in the region of the first reversal point and the second
reversal point.
The device according to the invention is characterized in that a measuring
means for
determining a position of the piston in the working space is provided, that at
least one
controllable valve is arranged, through which the pressure fluid can be led
into and/or out of
the working space and in that a control unit is provided which is connected to
the measuring
means and the at least one controllable valve, wherein by the control unit the
movement of
the piston in the working space can be controlled and changed.
A basic idea of the invention resides in abandoning a previous elaborate
mechanical control
of the piston in the working space and in providing for this an electrical or
electronic control
unit. According to the invention provision is made for at least one measuring
means for
determining the position of the piston in the working space. The measuring
means can
emit signals concerning position data of the piston in a continuous manner or
in
predetermined short time intervals. These signals or data are received by the
control
unit and processed as a function of a predetermined control logic, whereby
control
signals or control data are generated for one or several controllable valves.
Thus, by
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way of the at least one controllable valve pressure fluid can be led into and
out of the
working space in a selective manner.
Consequently, in the case of the device according to the invention there is no
need for
an elaborately produced working piston with a plurality of lines arranged
therein, This
reduces the expenditure in manufacturing to a considerable extent. Moreover,
the
movement behavior of the piston in the housing can now be controlled as well
as
changed in an especially easy way by changing or adapting the corresponding
control
logic in the control unit. In this way, the stroke and/or frequency of the
reversible move-
ment of the piston can be controlled and changed relatively easily.
For the device according to the invention basically all suitable controllable
valves can be
employed. According to a further development of the invention it is
particularly expedient for
the valve to be an electromagnetic valve. The valve body can be adjusted by an
electromagnetic arrangement between an open and a closed position. It is also
possible to
set intermediate positions, thus allowing the quantity of pressure fluid
supplied to the
working space to be set. Basically, any type of pressure fluid can be
provided, in which case
use is preferably made of hydraulic oil.
Likewise, concerning the measuring means these can be provided with all usable
sensors
for length or position measurement that operate, in particular, optically,
capacitively,
inductively, magnetically or in another way. According to an embodiment of the
invention it
is especially advantageous for the measuring means to have a linear sensor,
This is
particularly appropriate if the piston is moved linearly in the housing
between the two
reversal points.
A preferred embodiment variant of the invention resides in the fact that the
measuring
means has an elongate first measuring component which extends into the working
space
and into a free space in the piston. Thus, the measuring component is not
arranged behind
a wall of the housing but directly in the working space, in which the piston
moves. For a
particularly precise position measurement the elongate first measuring
component
protrudes into a corresponding free space in the piston, in which case the
piston preferably
slides contact-free along the first measuring component.
It is particularly expedient that in the free space of the piston a second
measuring com-
ponent, in particular a magnet, is arranged. The two measuring components
interact in
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such a way that a very precise position determination of the second measuring
compo-
nent and therefore of the piston relative to the first measuring component
arid thus rela-
tive to the working space and the housing can be effected. The first measuring
compo-
nent can have a coil, in which the magnet induces a current of e.g. 4 to 20 mA
as a
measure for the position of the piston.
Basically, the piston can be moved reversibly in the housing such that the
piston does
not contact the wall of the housing with its two front faces. In this way, the
device can be
employed as a so-called vibration generator. An advantageous embodiment of the
in-
vention resides in the fact that on at least one reversal point a percussion
surface is ar-
ranged, onto which the piston strikes specifically in order to generate a
percussive pulse.
Basically, a percussion surface can be arranged on both opposite front faces
of the
piston on the housing. By preference, however, only a single percussion
surface is
present so that specific percussive pulses can be generated as desired for
percussion
drilling for example.
According to a further variant of the invention it is preferred that by the
control unit a
frequency and/or a stroke of the piston can be set and adjusted. To change the
fre-
quency in particular the opening and closing times and, where appropriate, the
supply of
hydraulic energy can be set by the control unit. In addition, the stroke of
the piston can
be reached by changing the position of the two reversal points through a
corresponding
opening and closing of the controllable valves. For this purpose, the control
unit prefer-
ably has an input interface, such as an input field. In addition, the control
unit can be
actuated directly through a customary machine control from an operating unit
by an op-
erator.
Another preferred embodiment variant of the invention can be seen in the fact
that the
control unit has a program memory, in which different control programs for
controlling the
piston can be stored. For instance specific control programs can be stored for
particular
application purposes. For example at the beginning of a program a high
frequency with a
small piston stroke can be provided, whereas in the program sequence the
piston stroke
then increases and a frequency decreases over time. Provision can be made for
almost
any number of different program sequences to control the piston with regard to
frequency and stroke. For instance a program for quick advancement or a
particularly
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gentle driving process can be provided. In addition, programs for specific
types of soil
can be stored.
The invention comprises a construction machine which is characterized in that
the pre-
viously described device for generating percussive pulses or vibrations is
arranged. In
particular, the construction machine can be provided for foundation
engineering.
According to an embodiment of the invention it is especially advantageous for
the con-
struction machine to be an earth drilling apparatus. If the device is provided
for generat-
ing percussive pulses, percussion drilling can be carried out. This is
particularly advan-
tageous when penetrating harder layers of rock. Alternatively or additionally,
the device
can also be designed free from percussion contacts for the generating of
vibrations. In an
earth drilling apparatus with a drilling tool driven in a rotating manner so-
called over-
burden drilling can thus be carried out in particular. In this, the rotational
movement of the
drilling tool is superimposed by a vibratory or oscillatory movement. Through
super-
imposed vibrations a liquefaction of the ground, so to speak, can be achieved
at least in
the contact region with the drilling tool which leads to an improved drilling
progress.
Another embodiment of the invention can be seen in the fact that the
construction machine
is a pile driver or a vibrator. Such pile drivers or vibrators can be used
e.g. for the
introduction of steel beams, piles or sheet piles which are driven into the
ground through
percussive pulses or vibrations.
The method according to the invention is characterized in that the position of
the piston
is detected by way of a measuring means and that depending on the detected
position
of the piston a control unit controls at least one controllable valve, through
which pres-
sure fluid is led into and/or out of the working space, wherein by the control
unit the
movement of the piston is controlled.
The method according to the invention can be carried out, in particular, with
the previ-
ously described device. The advantages described beforehand are achieved
thereby.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of a device according to one embodiment.
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DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
The invention is described further hereinafter by way of a preferred
embodiment illus-
trated schematically in the accompanying drawing Figure 1.
In the single drawing a device 10 according to the invention is illustrated
which is de-
signed to generate percussive pulses. The device 10 has a housing 12 with a
cylindrical
working space 14, in which a piston 20 of approximately cylindrical shape is
supported in
a linearly movable manner such that it is reversible between two reversal
points. The
piston 20 is supported in a fluid-tight manner in the housing 12 and, as shown
in the
embodiment, can protrude with one side from the housing 12. With a free front
face 24
the piston 20 strikes onto a corresponding percussion surface 18 which can be
an inser-
tion end of a drill drive shaft.
In the region of the upper first reversal point a first opening 15 for a first
supply line 31 of
a pressure fluid supply 30 is provided on the housing 12. In the region of a
lower second
reversal point the working space 14 is connected through a second opening 16
to a
second supply line 32 of the pressure fluid supply 30, By means of a
controllable valve
36, which is designed as a 2/4 directional control valve in the illustrated
embodiment, the
two openings 15, 16 are alternately connected to a hydraulic pressure source P
and an
unpressurized disposal tank T. Through this, two opposite pressure chambers in
the
working space 14 are each alternately filled with pressure fluid and emptied
of the pres-
sure fluid. As a result, the piston 20 is set into a desired reversible
movement in the
housing 12.
According to the invention a measuring means 40 with a first elongate
measuring com-
ponent 42 is provided on the housing 12. The first measuring component 42 is
of bar-
shaped design and extends into the working space 14 and into a free space 22
arranged
correspondingly thereto in the piston 20. In the free space 22 in a lower
region thereof a
ring-shaped magnet is arranged as second measuring component 44. The second
measuring component 44 is firmly connected to the movable piston 20 while the
elongate first measuring component 42 is firmly attached to the housing 12.
The meas-
uring means 40 is designed e.g. as an inductive linear sensor which precisely
ascertains
the position of the second measuring component 44 and therefore of the piston
20
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with respect to the elongate first measuring component 42 and thus the
position of the
piston 20 in the working space 14.
Via a line connection 52 the measuring means 40 is connected to a control unit
50,
whereby analog signals or digital data on the current position of the piston
20 in the
working space 14 are transmitted. Depending on a predetermined program or
control
logic of the control unit 50 the controllable valve 36 is actuated via
electromagnetic ele-
ments 37 so that e.g. the first supply line 31 is connected to the
unpressurized tank T
and the second supply line 32 to the pressure source P, as illustrated in the
drawing.
When the valve 36 is switched over by the control unit 50 the pressure source
P can
then be connected to the first supply line 31 while the tank T is connected to
the second
supply line 32. In this valve position the lower region of the working space
14 is emptied
of pressure fluid while an upper region of the working space 14 is at the same
time filled
with pressure fluid, in which case the piston 20 then moves from the upper
first reversal
point downwards to the lower second reversal point. When the measuring means
40
establishes that a trigger point of the piston 20 has been reached in the
housing 12, a
switch-over of the valve 36 can then be effected again by the control unit 50
so that a
change of direction is brought about by actuating the electromagnetic elements
37 of the
controllable valve 36 via the control lines 54.
Through a corresponding change of the control logic in the control unit 50 the
frequency of
the piston 20 and the stroke of the piston 20 between the two reversal points
can be
changed and set without further ado.
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